"It was pretty scary", he told AAP when finally opening a beer, thankful his house came with sprinklers on the roof.

Westerly winds are expected to pick up again on Monday afternoon but will not be as extreme as conditions at the weekend.

NSW Police have launched an investigation into the cause of the fire and are appealing for witnesses.

New South Wales RFS said the blaze was "highly suspicious", with Commissioner Shane Fitzsimmons saying, "How dare anyone - if they are deliberately involved in lighting fires - endanger our firefighters and also [put] all these communities in harm's way".

Embers posed a serious threat to homes on Saturday night.

"Still quite a hard day ahead (on Monday)", he told Nine Network.

"We've got a lot of work ahead of us and some strong winds dominating the system today which are going to prove very problematic for the firefighters and all those people in and around this fire ground area", Commissioner Fitzsimmons said.

"Residents in the area of Sandy Point and Alfords Point should continue to monitor the conditions as they could change quickly", the RFS said in an alert at 6am.

The Transport Management Centre said Heathcote Road remained closed between New Illawarra Road and Macarthur Drive, and there was no forecast for when the road would be reopened.

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